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TY - CONF AU - Abbott, M.G. AU - Rehm, G. ED - Schaa, Volker RW ED - Jansson, Andreas ED - Shea, Thomas ED - Olander, Johan TI - Tune Computation via Model Fitting to Swept Machine Response Measurement J2 - Proc. of IBIC2019, Malmö, Sweden, 08-12 September 2019 CY - Malmö, Sweden T2 - International Beam Instrumentation Conferenc T3 - 8 LA - english AB - At Diamond Light Source we compute the horizontal and vertical tunes by fitting a simple multi-pole resonator model to the measured electron beam frequency response. The transverse (and longitudinal) tune response is measured by sweeping an excitation across the range of possible tune frequencies and synchronously measuring the IQ response. The multi-pole resonator model is a good fit to the measured behaviour, but the fitting process is surprisingly challenging. Problems include noisy measurements, very complex beam responses in the presence of increasing chromaticity, poor data when the beam is close to instability, and a number of challenges with the stability of the algorithm. The tune fitting algorithm now in use at Diamond has been developed and refined over many years. It is finally stable enough to work reliably throughout most beam operating conditions. The algorithm involves alternating peak finding and non-linear fitting, with a fairly naive mathematical approach; the main focus is on providing reliable results. PB - JACoW Publishing CP - Geneva, Switzerland SP - 482 EP - 486 KW - synchrotron KW - feedback KW - operation KW - betatron KW - resonance DA - 2019/11 PY - 2019 SN - 978-3-95450-204-2 DO - doi:10.18429/JACoW-IBIC2019-WECO03 UR - http://jacow.org/ibic2019/papers/weco03.pdf ER -